By Shane Chuning

I know I’m not the only one out there that has experienced broadheads and field points not hitting the same point.  I talk with a lot of guys and gals about this issue and we all have the same dilemma. As hunting season approaches, they sight in their broadheads and adjust their sight pins accordingly, then they don’t go back to field points until hunting season is over.

For many of us it can be a frustrating time of year when it comes time to put those broadheads on. Many of us will head up to the mountain or some honey hole we enjoy hunting and not practice shooting at camp, simply because we have moved everything for broadheads and they just don’t fly the same as those field points we have been shooting the whole year prior to the hunting season.

How many of us have been into an archery shop and purchased some arrows? They ask you what your draw length and draw weight is. They then cut your arrows within an inch of your draw length and give you 400 spine arrows for a 60lb bow or 340 to 350 spine arrows for a 70lb bow. That’s fine for a very general assumption, but usually far from the proper set up. Keep in mind how nice it would be for your broadheads to fly the same as your field points. My goal is to inform you of possible tuning problems that could be fixed and in return, make your experience with archery and hunting more enjoyable.

Testing the static spine of an arrow.

Archery is a very rewarding sport that can be stress relieving as well as relaxing. However, it can be very frustrating as well without the proper spined arrows or a well tuned bow. There are many factors that can contribute to some of these problems. Let’s start with a tuning overview.

  1. Check poundage and draw length of your bow. At the same time, you can check your timing as well. You want your cams rotating at the same time. Most manufactures will have some sort of timing marks for cam rotation. Check the owner’s manual. For you do-it-yourself guys, you can build a draw board which will show your cam rotation at full draw and give you your measured draw length.
  2. Determine your proper arrow length and point weight you will be using. This is where spine comes into play. Even as little as a ½” will change your spine and could make a big difference in your overall performance.
  3. Arrow manufactures will have shaft selection charts on the back of arrow boxes. This is just a rough general rule to go by in my opinion. There are too many factors to consider in spine selection on each individual bow and person, so I recommend finding an archery shop in your area that can lead you in the right direction. Don’t be afraid to ask some of these questions, it will only make you more informed with your equipment and give you an overall better experience.
  4. Check your limb tiller, which is your measurement from the inside of your limb pocket to your string. You will want this measurement to be the same between the two or at least within 1/8”.
  5. Setting up your arrow rest for your center shot and nock height position. General rule of thumb is to have the center of shaft to run with center of Berger hole. This is the threaded hole where your rest fastens to the riser. Your center shot is the left and right adjustment on your rest. Most manufactures will give you this measurement from the inside of riser to center of shaft. Look in your owner’s manual for this info. When not given as a measurement, you can sight your top cam with your bottom one, while keeping your string in view. Then with an arrow nocked, move the rest accordingly left to right, so they plane in together. This will give you a good starting point.
  6. Attach your nocking point. This coincides with your rest and your shaft lining up with the center of your Berger holes. Level to ¼” nock high is normal, depending on the type of bow you’re shooting. Some archers just use a d-loop for their nocking point, while others choose to use a brass nock with a d-loop. I prefer using a soft nock, which is BCY serving material. It’s lighter than a brass nock and just as easy to install. Being lighter means you’ll keep some of the speed lost by those brass nocks.
  7. Spray foot powder on the arrow rest and vanes. Make sure you use the powder and not the liquid. This will let you know if you are getting any type of vane contact on your rest. Vane contact is the cause of many tuning problems and I suggest you check for this. You will relieve a lot of headaches if you find this out ahead of time. A perfect bullet hole will not be achieved through paper without vane clearance.
  8. Vane contact can sometimes be eliminated as well by checking your nock position in relation to your vanes. You may find the need to rotating your nock slightly so your vanes clear the rest or cables, if needed.
  9. Shoot your arrow through paper from 6- to 7-feet. I like paper tuning in this range so you can catch the arrow in flight before your vanes correct any potential problems. You can learn a lot about yourself and your equipment from paper tuning. It will show you any flaws you or your equipment might have. For instance, grip torque, weak or stiff arrow spine, fletching contact, tiller adjustment, cam or idler wheel lean, center shot, and nock height are all possible problems to look for. Paper tuning is a very valuable tool and should not be overlooked in tuning.  After all, our goal is to have a well tuned bow.
  10. Bare shaft tuning is another method of tuning through paper. This method can also be rewarding, but takes a lot of patience. So, don’t get frustrated and make your adjustments in small increments at a time. You will be trying to achieve a perfect bullet hole as well with this method.
  11. Walk back tuning is one more method of tuning. This does not require shooting through paper. You simply mark a vertical line on your target, then shoot from 5-yards, 10-yards, 15-yards and 20-yards, etc. The farther you go, the more fine-tuned you are. Take your 20-yard pin and pick a spot on that vertical line in the upper third of the target. Shoot from the distances mentioned while aiming at the same spot every time. The idea is, you will end up with a vertical line of arrows. If you start varying from right to left, just move your rest in the opposite direction until you achieve that vertical line.

Bareshaft tuning results at 20 yards

Now that we have a rough overview on tuning a bow, I would like to talk more about arrow spine, probably one of the largest overlooked factors in tuning a bow. Arrow spine is measured when you take a 28” raw shaft and hang a 1.94 lb weight in the center. The amount of deflection your arrow produces is your arrow spine reading.

Many of us will confuse the spine of an arrow with the overall weight. For instance, you will hear people say they would like to shoot a heavier spined arrow. Heavier doesn’t necessarily mean a stiffer spined arrow. Let’s take Gold Tip Velocity Pro 300’s that are a 300 spined arrow, which weigh 8.5 grains per inch. Then say you have Carbon Express Maxima Hunter 350’s which weigh 8.9 grains per inch. You will see from the two arrows, weight and spine are completely different things. You can still have a light arrow with a stiffer spine.

Let’s look at the determining factors of arrow spine.

  1. The stiffness of the overall shaft material.
  2. The length of overall shaft.
  3. The tip weight.

There are two types of spine: static spine and dynamic spine. Static spine stays the same for the life of the arrow. Dynamic spine is the part that’s more important. This is measured upon the arrow being shot and the amount of energy stored in that particular bow; then transferred into the arrow causing the shaft to bend. The faster the bow, the more it bends during the shot; which is why there is such a wide range of spine selection.

A “Robin Hood” from 80 yards is the type of accuracy you can achieve by super-tuning your arrows and bow.

Shaft length will affect the dynamic spine. For instance, if you were to take a 2’ long ¼” dowel and put pressure at both ends by pushing inward on it, you would notice the deflection. Then take that same dowel and take ½” at a time off and apply pressure each and every time you change the length. There will definitely be a noticeable difference in the stiffness of that dowel. This is the same theory behind an arrow when shot with a bow.

Tip weight affects dynamic spine as well. The bow string pushes on the shaft at the time of the shot. Then there is an opposing force as well, pushing back at the shot. That is generally the field point or broadhead. The heavier the tip, the more force pushing back on that arrow shaft, thus weakening the spine of an arrow.

So keep in mind, tip weight is a big factor in getting a properly spined arrow. I hope this sheds some light on arrow spine and bow tuning. Remember to ask plenty of questions – you will be a better shot because you did. We also owe it to ourselves and the animals we hunt to know as much as we can about our equipment – in return making us all better archers in the long run.